diff --git a/content/html/document/src/ImageDocument.cpp b/content/html/document/src/ImageDocument.cpp
index 2bacbe9efc78..70e250a9a956 100644
--- a/content/html/document/src/ImageDocument.cpp
+++ b/content/html/document/src/ImageDocument.cpp
@@ -10,6 +10,7 @@
 #include "nsIImageLoadingContent.h"
 #include "nsGenericHTMLElement.h"
 #include "nsIDocumentInlines.h"
+#include "nsDOMTokenList.h"
 #include "nsIDOMHTMLImageElement.h"
 #include "nsIDOMEvent.h"
 #include "nsIDOMKeyEvent.h"
@@ -119,6 +120,13 @@ protected:
   void ResetZoomLevel();
   float GetZoomLevel();
 
+  enum eModeClasses {
+    eNone,
+    eShrinkToFit,
+    eOverflowing
+  };
+  void SetModeClass(eModeClasses mode);
+
   nsresult OnStartContainer(imgIRequest* aRequest, imgIContainer* aImage);
   nsresult OnStopRequest(imgIRequest *aRequest, nsresult aStatus);
 
@@ -421,8 +429,7 @@ ImageDocument::ShrinkToFit()
   // origin now that we're showing a shrunk-to-window version.
   (void) ScrollImageTo(0, 0, false);
 
-  imageContent->SetAttr(kNameSpaceID_None, nsGkAtoms::style,
-                        NS_LITERAL_STRING("cursor: -moz-zoom-in"), true);
+  SetModeClass(eShrinkToFit);
   
   mImageIsResized = true;
   
@@ -474,11 +481,10 @@ ImageDocument::RestoreImage()
   imageContent->UnsetAttr(kNameSpaceID_None, nsGkAtoms::height, true);
   
   if (mImageIsOverflowing) {
-    imageContent->SetAttr(kNameSpaceID_None, nsGkAtoms::style,
-                          NS_LITERAL_STRING("cursor: -moz-zoom-out"), true);
+    SetModeClass(eOverflowing);
   }
   else {
-    imageContent->UnsetAttr(kNameSpaceID_None, nsGkAtoms::style, true);
+    SetModeClass(eNone);
   }
   
   mImageIsResized = false;
@@ -514,13 +520,15 @@ ImageDocument::Notify(imgIRequest* aRequest, int32_t aType, const nsIntRect* aDa
     return OnStartContainer(aRequest, image);
   }
 
+  nsDOMTokenList* classList = mImageContent->AsElement()->GetClassList();
+  mozilla::ErrorResult rv;
   if (aType == imgINotificationObserver::DECODE_COMPLETE) {
     if (mImageContent) {
       // Update the background-color of the image only after the
       // image has been decoded to prevent flashes of just the
       // background-color.
-      mImageContent->SetAttr(kNameSpaceID_None, nsGkAtoms::_class,
-                             NS_LITERAL_STRING("decoded"), true);
+      classList->Add(NS_LITERAL_STRING("decoded"), rv);
+      NS_ENSURE_SUCCESS(rv.ErrorCode(), rv.ErrorCode());
     }
   }
 
@@ -528,8 +536,8 @@ ImageDocument::Notify(imgIRequest* aRequest, int32_t aType, const nsIntRect* aDa
     // mImageContent can be null if the document is already destroyed
     if (mImageContent) {
       // Remove any decoded-related styling when the image is unloaded.
-      mImageContent->UnsetAttr(kNameSpaceID_None, nsGkAtoms::_class,
-                               true);
+      classList->Remove(NS_LITERAL_STRING("decoded"), rv);
+      NS_ENSURE_SUCCESS(rv.ErrorCode(), rv.ErrorCode());
     }
   }
 
@@ -544,6 +552,25 @@ ImageDocument::Notify(imgIRequest* aRequest, int32_t aType, const nsIntRect* aDa
   return NS_OK;
 }
 
+void
+ImageDocument::SetModeClass(eModeClasses mode)
+{
+  nsDOMTokenList* classList = mImageContent->AsElement()->GetClassList();
+  mozilla::ErrorResult rv;
+
+  if (mode == eShrinkToFit) {
+    classList->Add(NS_LITERAL_STRING("shrinkToFit"), rv);
+  } else {
+    classList->Remove(NS_LITERAL_STRING("shrinkToFit"), rv);
+  }
+
+  if (mode == eOverflowing) {
+    classList->Add(NS_LITERAL_STRING("overflowing"), rv);
+  } else {
+    classList->Remove(NS_LITERAL_STRING("overflowing"), rv);
+  }
+}
+
 nsresult
 ImageDocument::OnStartContainer(imgIRequest* aRequest, imgIContainer* aImage)
 {
diff --git a/toolkit/themes/osx/global/media/TopLevelImageDocument.css b/toolkit/themes/osx/global/media/TopLevelImageDocument.css
index 8166b03c5175..8b77873efdd4 100644
--- a/toolkit/themes/osx/global/media/TopLevelImageDocument.css
+++ b/toolkit/themes/osx/global/media/TopLevelImageDocument.css
@@ -15,6 +15,14 @@
     color: #222;
   }
 
+  .overflowing {
+    cursor: -moz-zoom-out;
+  }
+
+  .shrinkToFit {
+    cursor: -moz-zoom-in;
+  }
+
   .completeRotation {
     transition: transform 0.3s ease 0s;
   }
diff --git a/toolkit/themes/windows/global/media/TopLevelImageDocument.css b/toolkit/themes/windows/global/media/TopLevelImageDocument.css
index 8166b03c5175..8b77873efdd4 100644
--- a/toolkit/themes/windows/global/media/TopLevelImageDocument.css
+++ b/toolkit/themes/windows/global/media/TopLevelImageDocument.css
@@ -15,6 +15,14 @@
     color: #222;
   }
 
+  .overflowing {
+    cursor: -moz-zoom-out;
+  }
+
+  .shrinkToFit {
+    cursor: -moz-zoom-in;
+  }
+
   .completeRotation {
     transition: transform 0.3s ease 0s;
   }